Superconductive quantum interference element

ABSTRACT

In a superconductive quantum interference element comprising Josephson joints, a washer coil and a detecting coil constituting a superconductive loop and a feedback modulation coil, to provide a superconductive quantum interference element capable of promoting spatial resolution by preventing an effective detection area of the detecting coil from enlarging even when a width of a superconductive wiring constituting the detecting coil and a superconductive film at a vicinity of the detecting coil are larger than an inner diameter of the detecting coil, there is constructed a superconductive quantum interference element having a structure provided with a slit at a detecting coil and or a superconductive film at a periphery of the detecting coil.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a magnetism measuring apparatus for measuring or observing an amount of magnetism in a range to a degree of micrometer with regard to a sample comprising various element or material such as various semiconductor element or semiconductor material or superconductive material, or metal material or inorganic material, particularly relates to a superconductive quantum interference element (hereinafter, referred to as SQUID) having a high resolution for detecting magnetism.

[0003] 2. Description of the Related Art

[0004] Recently, there has been reduced into practice, a high sensitivity magnetic flux meter having a spatial resolution to a degree of micrometer which is referred to as a SQUID microscope and there has frequently been carried out measurement or observation by using a SQUID microscope with regard to various element or material. SQUID is applied conventionally as a magnetism sensor having a high magnetic field resolution and when SQUID is used as a SQUID microscope for observing magnetism of a very small region, the spatial resolution becomes an important function.

[0005]FIGS. 2A and 2B is an outline circuit pattern diagram showing an example of conventional SQUID in consideration of spatial resolution. The SQUID is DC-SQUID fabricated by a superconductive loop 10 and a feedback modulation coil 20. FIG.3 shows an outline equivalent circuit diagram of the superconductive loop 10 shown in FIG. 2A. The superconductive loop 10 is constituted by a washer coil 11, two Josephson joints 12 and a detecting coil 13. As shown by FIGS. 2A, the superconductive loop 10 is integrated on a silicon substrate along with the feedback modulation coil 20.

[0006] As the Josephson joint 12, there is frequently used a tunnel junction type Josephson junction of niobium/aluminum oxide/niobium.

[0007] The feedback modulation coil 20 is magnetically coupled with the washer coil 11. Numeral 16 designates a contact hole of the detecting coil 13 and the washer coil 11.

[0008] In FIG. 2A and FIG. 3, by an outside control circuit, pertinent bias current is applied between two electrodes 21 a and 21 b of the washer coil 11 in directions designated in FIG. 3 and magnetic flux having an amount the same as that of magnetic flux detected by the detecting coil 13 and in direction reverse thereto, is fed back to the washer coil 11 via the feedback modulation coil 20 ( not illustrated in FIG. 3 ) overlapping the loop of the washer coil 11 to thereby drive thereof. Thereby, the magnetic flux detected by the detecting coil 13 can be provided from the outside control circuit as a voltage output.

[0009] The spatial resolution is determined by a shape such as a size of the detecting coil constituting SQUID and a distance between a sample and SQUID. When SQUID having high spatial resolution is designed and fabricated, SQUID is fabricated by designing an effective detection area of the detecting coil as small as possible and utilizing the thin film fabricating technology by using the photolithography technology.

[0010] According to the related art SQUID, described above, when the detecting coil is intended to fabricate to be small in order to promote the spatial resolution, in comparison with an inner diameter of the detecting coil, a width of the detecting coil per se and a superconductive film at a vicinity of the detecting coil are enlarged relatively. Then, there poses a problem that other than magnetism coupled to the inner diameter portion of the detecting coil, there is detected portions of magnetic flux repulsed by the dimagnetism of the detecting coil per se or the superconductive film at a vicinity of the detecting coil, as a result, an effective area of the detecting coil is enlarged.

SUMMARY OF THE INVENTION

[0011] It is a problem of the invention to resolve the above-described problem and to provide SQUID reducing an effective detection area of a detecting coil and promoting spatial resolution.

[0012] (First Means)

[0013] According to the invention, in order to resolve the above-described problem, there is constituted SQUID having a slit for passing a magnetic flux directed to the detecting coil in a magnetic flux repulsed by a superconductive film at either or both of the detecting coil and the superconductive film at a periphery of the detecting coil.

[0014] (Second Means)

[0015] In addition to the first means, there is used a beam machining apparatus as apparatus of machining the slit.

[0016] According to SQUID by the first means, in the magnetic flux repulsed by the detecting coil and/or the superconductive film at the periphery of the detecting coil, a portion of extra magnetic flux which is going to couple with the detecting coil, passes through the slit without being coupled to the detecting coil and therefore, coupling of the extra magnetic flux to the detecting coil is reduced and therefore, the effective detection area of the detecting coil can be reduced and the spatial resolution can be promoted.

[0017] By the second means, micromachining of the slit can be carried out and therefore, the function of excluding the extra magnetic flux coupled to the detecting coil can be promoted and the spatial resolution can further be promoted.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1A is an outline view illustrating a total structure of SQUID showing Embodiment 1 of the invention;

[0019]FIG. 1B is an outline view illustrating a structure of a detecting coil of SQUID showing Embodiment 1 of the invention;

[0020]FIG. 2A is an outline view showing an example of SQUID in consideration of the related art spatial resolution;

[0021]FIG. 2B is an outline view illustrating a structure of a detecting coil of SQUID shown in FIG. 2A;

[0022]FIG. 3 is an outline equivalent circuit diagram of a superconductive loop for detecting magnetism; and

[0023]FIG. 4 is an outline view illustrating a structure of a detecting coil of SQUID showing other embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] An explanation will be given of embodiments of the invention in reference to the drawings as follows.

[0025] (Embodiment 1 )

[0026]FIGS. 1A and 1B are outline views illustrating a structure of SQUID showing Embodiment 1 of the invention.

[0027]FIG. 1A shows a total structure of SQUID and FIG. 1B shows a structure of a vicinity of a detecting coil.

[0028] Similar to the conventional example, the superconductive loop 10 is constituted by the washer coil 11, the two Josephson joints 12 and the detecting coil 13 and is fabricated on a silicon substrate along with the feedback modulation coil 20.

[0029] Thereafter, by using a beam machining apparatus capable of carrying out micromachining, superconductive films at an upper layer and a lower layer of a portion of a slit 15 are deleted. The slit 15 is cut in parallel with the inner diameter shape of the detecting coil 13. Although as the beam machining apparatus used for machining the slit 15, there is used a focused ion beam machining apparatus, other beam machining apparatus such as excimer laser may be used, further, the slit 15 may be fabricated by using the photolithography technology.

[0030] When there is present a magnetic field in a direction perpendicular to a film at a periphery of the detecting coil, magnetic flux which is going to intersect with a portion of a superconductive member below the slit 15 in FIG. 1B, is repulsed by the characteristic of the complete dimagnetism of the superconductive member and diverged in a radial shape. There is constructed a structure in which magnetic flux directed in a direction of the detecting coil in the diverged magnetic flux, passes through the slit 15 and is drawn to an opposed side of the film. By cutting the slit 15 in parallel with the inner diameter shape of the detecting coil 13 in FIG. 1B, the magnetic flux directed to the detecting coil 13 can be made to pass through further efficiently. Although in FIG. 1B, the slit is provided at the superconductive film at a periphery of the detecting coil, slits may further be provided at the detecting coil per se as shown by FIG. 4. As shown by FIG. 4, the slits in this case may be slits in an orthogonal direction of a coil frame or may be slits in parallel with the coil frame. In either of the cases, these slits serve to pass the magnetic flux directed to the detecting coil in the magnetic flux repulsed by the detecting coil or the superconductive film at the periphery of the detecting coil.

[0031] Although fabricated SQUID is of an integrated type fabricated with the detecting coil in a single superconductive loop along with the washer coil and the Josephson joints, there may be constructed SQUID of a trans coupling type constituting a structure in which the detecting coil is formed by a superconductive loop other than the washer coil and a magnetic field detected by the detecting coil is coupled to the washer coil.

[0032] According to the invention, a portion of the magnetic flux repulsed by the dimagnetism of the detecting coil per se or the superconductive film at the vicinity of the detecting coil, passes through the slit and therefore, the portion dose not couple with the detecting coil, as a result, the effective area of the detecting coil can be prevented from enlarging. 

What is claimed is:
 1. A superconductive quantum interference element which is a superconductive quantum interference element fabricated by a photolithography technology and comprising a Josephson joint, a washer coil and a detecting coil constituting a superconductive loop and a feedback modulation coil, wherein there is provided a slit for passing a magnetic flux directed to the detecting coil in a magnetic flux repulsed by a supercondctive film at either or both of the detecting coil and the superconductive film at a periphery of the detecting coil.
 2. A superconductive quantum interference element which is a superconductive quantum interference element fabricated by a photolithography technology and comprising a Josephson joint and a washer coil constituting a first superconductive loop and a detecting coil and an input coil constituting a second superconductive loop magnetically coupled to the first conductive loop, and feedback modulation coil, wherein there is provided a slit for passing a magnetic flux directed to the detecting coil in a magnetic flux repulsed by a superconductive film at either or both of the detecting coil and the superconductive film at a periphery of the detecting coil.
 3. The superconductive quantum interference element according to claim 2; wherein the slit is machined by a beam machining apparatus.
 4. The superconductive quantum interference element according to claim 1; wherein the slit is machined by a beam machining apparatus. 